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OriginOfSpecies - 475 Rows
Column Type #Values Column Stats
id int(11) 475 Column Stats
subject varchar(80) 14 Column Stats
title varchar(250) 139 Column Stats
ordinal int(11) 30 Column Stats
description text 474 Column Stats

475 rows, page 12 of 119 (4/p)
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04 - Natural Selection 04-09 - Circumstances favourable for the production of new forms through Natural Selection 90 Throughout a great and open area, not only will there be a better chance of favourable variations, arising from the large number of individuals of the same species there supported, but the conditions of life are much more complex from the large number of already existing species; and if some of these many species become modified and improved, others will have to be improved in a corresponding degree, or they will be exterminated.

Each new form, also, as soon as it has been much improved, will be able to spread over the open and continuous area, and will thus come into competition with many other forms.

Moreover, great areas, though now continuous, will often, owing to former oscillations of level, have existed in a broken condition; so that the good effects of isolation will generally, to a certain extent, have concurred.

Finally, I conclude that, although small isolated areas have been in some respects highly favourable for the production of new species, yet that the course of modification will generally have been more rapid on large areas; and what is more important, that the new forms produced on large areas, which already have been victorious over many competitors, will be those that will spread most widely, and will give rise to the greatest number of new varieties and species.

They will thus play a more important part in the changing history of the organic world. In accordance with this view, we can, perhaps, understand some facts which will be again alluded to in our chapter on Geographical Distribution; for instance, the fact of the productions of the smaller continent of Australia now yielding before those of the larger Europaeo-Asiatic area.

Australia
Australia

Europe
Europe

Asia
Asia


Thus, also, it is that continental productions have everywherebecome so largely naturalised on islands.

On a small island, the race for life will have been less severe, and there will have been less modification and less extermination.
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04 - Natural Selection 04-11 - Divergence of Character 90 After the foregoing discussion, which has been much compressed, we may assume that the modified descendants of any one species will succeed so much the better as they become more diversified in structure, and are thus enabled to encroach on places occupied by other beings. Now let us see how this principle of benefit being derived from divergence of character, combined with the principles of natural selection and of extinction, tends to act.
04 - Natural Selection 04-12 - On the Degree to which Organisation tends to advance 90 The three lowest orders of mammals, namely, marsupials, edentata, and rodents, co-exist in South America in the same region with numerous monkeys, and probably interfere little with each other.

kangaroo
kangaroo

armadillo
armadillo

rat
rat

monkey
monkey

South America
South America


Although organisation, on the whole, may have advanced and be still advancing throughout the world, yet the scale will always present many degrees of perfection; for the high advancement of certain whole classes, or of certain members of each class, does not at all necessarily lead to the extinction of those groups with which they do not enter into close competition.

In some cases, as we shall hereafter see, lowly organised forms appear to have been preserved to the present day, from inhabiting confined or peculiar stations, where they have been subjected to less severe competition, and where their scanty numbers have retarded the chance of favourable variations arising.
05 - Laws of Variation 05-12 - Reversion to Long Lost Characters 90 What now are we to say to these several facts?

We see several distinct species of the horse-genus becoming, by simple variation, striped on the legs like a zebra, or striped on the shoulders like an ass. In the horse we see this tendency strong whenever a dun tint appears- a tint which approaches to that of the general colouring of the other species of the genus.

horse
horse

ass
ass

Dun Horse
Dun Horse


The appearance of the stripes is not accompanied by any change of form or by any other new character.

We see this tendency to become striped most strongly displayed in hybrids from between several of the most distinct species.

Now observe the case of the several breeds of pigeons: they are descended from a pigeon (including two or three sub-species or geographical races) of bluish colour, with certain bars and other marks; and when any breed assumes by simple variation a bluish tint, these bars and other marks invariably reappear; but without any other change of form or character.

pigeon
pigeon


When the oldest and truest breeds of various colours are crossed, we see a strong tendency for the blue tint and bars and marks to reappear in the mongrels.

I have stated that the most probable hypothesis to account for the reappearance of very ancient characters, is- that there is a tendency in the young of each successive generation to produce the long-lost character, and that this tendency, from unknown causes, sometimes prevails.

And we have just seen that in several species of the horse-genus the stripes are either plainer or appear more commonly in the young than in the old.

Call the breeds of pigeons, some of which have bred true for centuries, species; and how exactly parallel is the case with that of the species of the horse-genus!

horse
horse

pigeon
pigeon


For myself, I venture confidently to look back thousands on thousands of generations, and I see an animal striped like a zebra, but perhaps otherwise very differently constructed, the common parent of our domestic horse (whether or not it be descended from one or more wild stocks), of the ass, the hemionus, quagga, and zebra.

horse
horse

ass
ass

hemionus
hemionus

quagga
quagga

zebra
zebra